1. Field of the Invention
The present invention relates to a ratchet tensioner used to provide an appropriate tension to a timing belt or a timing chain of a vehicle engine, and more particularly to a ratchet tensioner having a mechanism for locking and releasing a plunger.
2. Description of the Related Art
The ratchet tensioner has been widely used for suppressing vibrations generated when a timing belt or a timing chain is traveling to transmit rotation between a crankshaft and a camshaft of an engine, and for maintaining an appropriate tension in the timing belt or chain. Such ratchet tensioner is constructed such that a plunger protruding from a housing of the tensioner presses the rear side of a free end portion of a tensioner lever pivotally mounted to a body of the engine, so that a shoe surface of the tensioner lever slidably contacts with a slack side of the chain to give an appropriate tension to the chain (see Japanese Patent Publication No. HEI-3-8415, Japanese Patent Laid-Open Publication No. HEI-10-2386, and Japanese Patent Laid-Open Publication No. HEI-11-344086).
A typical example of the known ratchet tensioners is shown in FIGS. 6 and 7. The tensioner 31 includes a housing 32, a plunger 33 slidably mounted in the housing 32 and urged by a plunger spring 36 so that one end 33A of the plunger 33 projects outward from the front surface of the housing 32. The tensioner 31 further has a ratchet pawl body 34 pivotally mounted by a shaft 34A to the housing 32. The ratchet pawl body 34 is received in a recess 32E defined between opposed side walls 32C, 32D in the housing 32, and urged by a ratchet pawl spring 38. The ratchet pawl body 34 has a ratchet pawl 34B engaged with a ratchet tooth 33B formed on a side surface of outer periphery of the plunger, so that a backward displacement of the plunger 33 is suppressed.
The ratchet tensioner 31 includes a buffer mechanism using a flow resistance of oil, and a backlash is maintained between the ratchet tooth 33B and the ratchet pawl 34B, so that the oil (not shown) is introduced into the interior of the plunger 33 from an external oil pump operating in synchronism with the engine via a check valve mechanism 35. When the plunger 33 receives shock from the tensioner lever, the plunger 33 is retracted against the force of a plunger spring 36 within a range of the backlash in a state that the ratchet tooth 33B and the ratchet pawl 34B are engaged. At that time, the check valve mechanism 35 is closed to leak the oil in the plunger 33 from between the outer peripheral surface of the plunger 33 and the inner peripheral surface of a plunger-accommodating hole of the housing 32, so that a shock force is relieved. Furthermore, reference numeral 32B in FIGS. 6 and 7 indicates a mounting hole for mounting the ratchet tensioner 31 to the engine body.
Additionally, the ratchet tensioner 31 comprises a plate 37 secured to an end of the shaft 34A of the ratchet pawl body projecting outside the housing 32. When the ratchet tensioner 31 is shipped or to be mounted to the engine, as shown in FIGS. 8 and 9, a stopper pin 39 is inserted into a pin inserting hole 37A of the plate 37 to contact with an outer wall end surface 32A of the housing 32 in a state that the ratchet tooth 33B and the ratchet pawl 34B are engaged, and thus the plunger 33 is retained so as not to fly out from the housing 32. In this case, after mounting the ratchet tensioner 31 to the engine, the stopper pin 39 is removed to place the tensioner 31 in an operating condition.
Furthermore, as other means for holding the plunger 33 in position against movement in the projecting direction when shipping the ratchet tensioner, as shown in FIGS. 10 and 11, the ratchet pawl body 34 is rotated by the rotation of the outer plate 37 to engage the ratchet tooth 33B with the ratchet pawl 34B, and then the stopper pin 39 is inserted through the pin inserting hole 37A of the outer plate 37 into a stopper hole 32C formed in the housing 32.
In the ratchet tensioner, it is necessary to pull in the plunger 33 that has been projected in case of repairing the engine, removing or mounting the chain. However, the prior ratchet tensioner has problems that the plunger 33 cannot be pushed simply into the interior of the housing, and the work for removing or mounting the chain cannot be performed simply, since the outer plate 37 is rotated to rotate the ratchet pawl body 34 so that it is possible to release the engagement of the plunger 33 serving as one-way mechanism, but there is not a mechanism for maintaining the state in that the engagement is released. Furthermore, it is difficult to insert a driver from a small window hole such as an engine service hole etc., for rotating the outer plate, and it is not capable of maintaining the disengagement state of the plunger. The ratchet tensioner further has problem that an extra component is necessary since the outer plate, which is a separate member, is mounted to a ratchet shaft secured to the ratchet pawl body.
Therefore, in view of the aforementioned problems, an object of the present invention is to provide a ratchet tensioner which is capable of rotating a ratchet pawl body in a direction to engage a ratchet pawl with a ratchet tooth formed on a plunger, thereby maintaining the plunger in its engaged state, or being capable of rotating the ratchet pawl body in the other direction to disengage a ratchet pawl from a ratchet tooth on the plunger, thereby easily releasing the engagement of the plunger and easily maintaining the plunger in its disengaged state, or being capable of rotating the ratchet pawl body in a direction or the other direction to engage a ratchet pawl with a ratchet tooth on a plunger, thereby maintaining the plunger in its engaged state or being capable of rotating the ratchet pawl body in the other direction to disengage a ratchet pawl with a ratchet tooth on the plunger, thereby easily releasing the engagement of the plunger and easily maintaining the plunger in its disengaged state.
To accomplish the above object, according to a first aspect of the present invention, there is provided a ratchet tensioner comprising: a housing having two opposed side walls defining therebetween a recess; a plunger retractably mounted in the housing with one end projecting outward from the housing, the plunger having a series of ratchet teeth formed on an outer peripheral surface of the plunger, a plunger spring acting between the housing and the plunger and urging the plunger in a direction to project outward from the housing; a ratchet pawl body received in the recess of the housing and pivotally mounted by a shaft to the housing, the ratchet pawl body having a ratchet pawl formed at one end of the ratchet pawl body; a ratchet pawl spring acting between the housing and the ratchet pawl body and urging the ratchet pawl body to turn about the axis of the shaft in a direction to engage the rachet pawl with the ratchet teeth on the plunger, thereby preventing the plunger from moving backward; and a plunger locking mechanism for locking the plunger in position against movement relative to the housing. The plunger locking mechanism has a lever-like pin contact portion formed integrally with the other end of the ratchet pawl body, a pin member-fitting hole formed in the opposed side walls of the housing in registry with the lever-like pin contact portion of the ratchet pawl body such that there being two pin-accommodating spaces defined between the lever-like pin contact portion and an inner peripheral surface of the pin member-fitting hole on opposite sides of the lever-like pin contact portion, and a pin member removably inserted in one of the pin-accommodating spaces to turn the ratchet pawl body in one direction to keep the engagement between the ratchet pawl and the ratchet teeth on the plunger.
According to a second aspect of the present invention, there is provided a ratchet tensioner comprising: a housing having two opposed side walls defining therebetween a recess; a plunger retractably mounted in the housing with one end projecting outward from a surface of the housing, the plunger having a series of ratchet teeth formed on an outer peripheral surface of the plunger; a plunger spring acting between the housing and the plunger and urging the plunger in a direction to project outward from the housing; a ratchet pawl body received in the recess of the housing and pivotally mounted by a shaft to the housing, the ratchet pawl body having a ratchet pawl formed at one end of the ratchet pawl body; a ratchet pawl spring acting between the housing and the ratchet pawl body and urging the ratchet pawl body to turn about the axis of the shaft in a direction to engage the rachet pawl with the ratchet teeth on the plunger, thereby preventing the plunger from moving backward; and a plunger releasing mechanism for releasing the plunger from locking engagement with the ratchet pawl. The plunger releasing mechanism has a lever-like pin contact portion formed integrally with the other end of the ratchet pawl body, a pin member-fitting hole formed in the opposed side walls of the housing in registry with the lever-like pin contact portion of the ratchet pawl body such that there being two pin-accommodating spaces defined between the lever-like pin contact portion and an inner peripheral surface of the pin member-fitting hole on opposite sides of the lever-like pin contact portion, and a pin member removably inserted in one of the pin-accommodating spaces to turn the ratchet pawl body in the opposite direction to disengage the ratchet pawl from the ratchet teeth on the plunger against the force of the ratchet pawl spring, thereby allowing the plunger to project outward from the housing by the force of the plunger spring.
According to a third aspect of the present invention, there is provided a ratchet tensioner comprising: a housing having two opposed side walls defining therebetween a recess; a plunger retractably mounted in the housing with one end projecting outward from a surface of the housing, the plunger having a series of ratchet teeth formed on an outer peripheral surface of the plunger; a plunger spring acting between the housing and the plunger and urging the plunger in a direction to project outward from the housing; a ratchet pawl body received in the recess of the housing and pivotally mounted by a shaft to the housing, the ratchet pawl body having a ratchet pawl formed at one end of the ratchet pawl body; a ratchet pawl spring acting between the housing and the ratchet pawl body and urging the ratchet pawl body to turn about the axis of the shaft in a direction to engage the rachet pawl with the ratchet teeth on the plunger, thereby preventing the plunger from moving backward; and a plunger locking and releasing mechanism for selectively locking and releasing the plunger relatively to the ratchet pawl. The plunger locking and releasing mechanism has a lever-like pin contact portion formed integrally with the other end of the ratchet pawl body, a pin member-fitting hole formed in the opposed side walls of the housing in registry with the lever-like pin contact portion of the ratchet pawl body such that there being two pin-accommodating spaces defined between the lever-like pin contact portion and an inner peripheral surface of the pin member-fitting hole on opposite sides of the lever-like pin contact portion, and a pin member removably and selectively inserted in the pin-accommodating spaces such that when the pin member is inserted in one of the two pin-accommodating spaces, the ratchet pawl body is turned in one direction to keep the engagement between the ratchet pawl and the ratchet teeth on the plunger, thereby locking the plunger in position against movement relative to the housing, and when the pin member is inserted in the other pin-accommodating space, the ratchet pawl body is turned in the opposite direction to disengage the ratchet pawl from the ratchet teeth on the plunger against the force of the ratchet pawl spring, thereby allowing the plunger to project outward from the housing by the force of the plunger spring.
In the ratchet tensioner provided in accordance with the first aspect of the present invention, when the pin member is inserted into one of the two spaces formed between the pin contact portion of the ratchet pawl body and the peripheral edge of the pin member-fitting hole, the ratchet pawl body is turned in the direction to keep the meshing engagement between the ratchet pawl and the ratchet tooth on the plunger. Thus the plunger is locked in position against movement relative to the housing.
In the ratchet tensioner provided in accordance with the second aspect of the present invention, when the pin member is inserted into one of the two spaces formed between the pin contact portion of the ratchet pawl body and the peripheral edge of the pin member-fitting hole, the ratchet pawl body is turned in one direction to disengage the ratchet pawl from the ratchet tooth on the plunger against the force of the ratchet pawl spring, thereby allowing the plunger to project from the housing by the force of the plunger spring.
In the ratchet tensioner provided in accordance with the third aspect of the present invention, when the pin member is inserted in one of the two pin-accommodating spaces, the ratchet pawl body is turned in one direction to keep the engagement between the ratchet pawl and the ratchet teeth on the plunger, thereby locking the plunger in position against movement relative to the housing, and when the pin member is inserted in the other pin-accommodating space, the ratchet pawl body is turned in the opposite direction to disengage the ratchet pawl from the ratchet teeth on the plunger against the force of the ratchet pawl spring, thereby allowing the plunger to project outward from the housing by the force of the plunger spring.